Electrodes are indispensable and of importance in the fields of chemical analysis and electrochemical industries. The development about the material of an electrode for practical application is continuously lasting. A good electrode must possess a superior electric conductivity, an excellent catalytic activity to an chemical reaction expected to occur, and a sufficiently prolonged life-time to be free from being easily spoiled or damaged. An electrode will face much crucial conditions when applied as an anode electrode. In addition to an abrasion caused thereonto by its surrounding solution, the anode electrode will be eroded by oxygen or chlorine gas formed thereon. Furthermore, a pure metal or a graphite anode electrode will be easily worn out by participating by itself in the electrolytic reaction. The life-time of the electrode is accordingly shortened.
Owing to the possibility of possessing a superior electrochemically catalytic activity, excellent electric conductivity, corrosion durability and chemical inertness, the metal oxide coated electrode has attracted many people's attention for years. After a report that a metal oxide coated electrode was successfully fabricated was revealed in Refs. 1 and 2 by Beer in 1972 and 1973, different types of metal oxide coated electrodes, such as TiO.sub.2, V.sub.2 O.sub.5, Nb.sub.2 O.sub.5, MnO.sub.2, RuO.sub.2, IrO.sub.2, SnO.sub.2, PbO.sub.2, etc., were subsequently disclosed. Some of these metal oxide coated electrodes are applied in real electrochemical processes such as saline electrolysis, production of alkali chloride, treatment or recycling of metal-containing waste water, electrochemical synthesis of organic compounds, and decomposition of organic compounds, as disclosed in Refs. 3-6. The above-mentioned metal oxide coated electrodes are affordable to replace the graphite electrode which is apt to be decomposed in a hydrochloric acid solution even being dilute as disclosed in Ref. 7, or the platinum electrode which is used to be dissolved to form a salt in same as disclosed in Ref. 8. Some other metal electrodes, such as Ti, Nb, and Ta electrodes can be another alternatives. However, due to their high costs or their tendency to form inactive films on their surfaces and give rise to their electric resistances so as to weaken the applied current density therethrough, those metal electrodes are still unacceptable in industry.
Iridium, palladium, and their oxides possess an excellent catalytic activity. Iridium oxide has been utilized in an acidic hydro-electrolytic reaction, as disclosed in Refs. 9 and 10. Palladium is always adopted as a catalyst in the chemical industry and has been tried to be coated on platinum and glass carbon, as disclosed in Ref. 11, or co-plated with iridium oxide on glass carbon by an electrochemical process, as disclosed in Ref. 12. The methods for manufacturing an iridium oxide coated electrode have been priorly reported, such as vacuum reactive sputtering as disclosed in Refs. 13-15, constant voltametric cyclic oxidation from pure iridium as disclosed in Refs. 16 and 17, pyrolysis as disclosed in Refs. 18-21, electrochemically cyclic voltametry as disclosed in Refs. 12 and 22-24, plasma fusion as disclosed in Ref. 25, and laser coating as disclosed in Ref. 26, etc. The iridium oxide coated electrode manufactured by any one of the above-mentioned methods except the electrochemical method, is easily damaged due to a non-uniformed grain size distribution on the surface of the obtained electrode, and is likely dissolved in an acid solution when the applied voltage reaches a high value of about 1.6 V with respect to the standard hydrogen electrode so that the iridium oxide coated electrode will be improper as a catalyst under this condition, as disclosed in Ref. 27.
The above-mentioned references are listed as follows and hereinbefore called Ref. 1-27 respectively:
1. H. B. Beer et al., U.S. Pat. No. 3,711,385 (1973). PA0 2. H. B. Beer et al., U.S. Pat. No. 3,632,498 (1972). PA0 3. B. Beden, F. Kadirgan, C. Lamy and J. M. Leger, J. Electroanal. Chem., 127, 75 (1981). PA0 4. R. R. Adzic, M.D. Spasojevic, and A. R. Despic, J. Electroanal. Chem., 92, 31 (1978). PA0 5. A. Capon and R. Parsons, Electroanal. Chem. and Interfacial Electrothem., 45,205 (1973). PA0 6. P. Ocon, B. Beden, H. Huser and C. Lamy, Electrochim. Acta, 32(3), 387 (1987). PA0 7. L. E. Vaaler, Electrothem. Technol., 5, 170 (1967). PA0 8. A. Visintin, W. E. Triaca, and A. J. Arvia, J. Electroanal. Chem., 284, 65 (1990 ) PA0 9. A. Nidola, "Electrodes of Conductive Metallic Oxides", S. Trasatti ed., Elesvier, Amsterdam, Chapter 11,627 (1980). PA0 10. S. Hackwood, L. M. Schiavone, W. C. Dautremont Smith and G. Beni, J. Electrochem. Soc., 128(12), 2569 (1981). PA0 11. R. Le Penven, W. Levason and D. Pletcher, J. Appl. Electrochem., 20, 399 (1990). PA0 12. J. A. Cox, S. E. Gadd and B. K. Das, J. Electroanal. Chem., 256, 199(1988). PA0 13. K. S. Kang and J. L. Shay, J. Electrochem. Soc., 130(4), 766 (1983). PA0 14. R. Kotz, H. Neff and S. Stucki, J. Electrochem. Soc., 131 (1), 72 (1984). PA0 15. R. Sanjines, A. Aruchamy and F. Levy, J. Electrochem. Soc., 136(6), 40(1989). PA0 16. B. E. Conway and J. Mozota, Electrochimica Acta, 28, 1 (1983). PA0 17. J. Mozota and B. E. Conway, Electrochimica Acta, 28, 9 (1983). PA0 18. J. C. F. Boodts and S. Trasatti, J. Appl. Electrochem., 19, 255 (1989). PA0 19. G. Lodi, A. D. Battisti, G. Bordin, C. D. Asmundis and A. Benedetti, J. Electroanal. Chem., 277, 139 (1990). PA0 20. E. N. Balko and P. H. Nguyen, J. Appl. Electrochem., 21, 678 (1991). PA0 21. S. Ardizzone, M. Falciola and S. Trasatti, J. Electrochem. Soc., 6(5), 1545 (1989). PA0 22. J. A. Cox and R. K. Jaworski, J. Electroanal. Chem., 281, 163 (1990). PA0 23. F. Colom, J. H. Gonzalez and J. Peinado, J. Electroanal. Chem., 89, 397 (1978). PA0 24. E. M Kelliher and T. L. Rose, J. Electrochem. Soc., 136(6), 1765 (1989). PA0 25. K. Schnider, B, Jahnke, R. Btirgel, and J. Ellner, Mat. Sci. and Tech., 1,613 (1985). PA0 26. A. Kar and J.Mazumder, Metall. Trans. A, 20A, 363 (1969). PA0 27. D. Michell, D. A. J. Rand, and R. Woods, J. Electroanal. Chem, 84, 117 (1977).
The shortages of the prior graphite electrode, metal electrodes, and metal oxide coated electrodes are listed as follows:
1. The anti-corrosive property of the prior electrodes are poor; PA1 2. The prior electrodes are easily oxidized; PA1 3. The catalytic activity of the prior electrodes is unstable and unsatisfactory; PA1 4. The manufacture of the prior electrodes is costly.
It is therefore attempted by the Applicant to deal with the shortages encountered by the prior art.